In the field of automated machining, a numerically controlled machine tool positioning system is often used in conjunction with a probe sensor to measure certain features of a workpiece that is to be drilled, cut, welded or machined. During a probing cycle, either the workpiece or the probe is moved by the positioning system until contact between the workpiece and probe occurs. Upon contact the probing system provides a "trip" signal input to the positioning system regarding the location of the workpiece. Typically, the probe sensor is a mechanical stylus or other contact probe. The probe has to be made compliant enough to withstand accidental shocks and overtravel, but still be stiff enough for repeated probe cycles. When used in laser drilling applications, the probe must be displaced from the drilling light path to prevent destruction of the probe by the laser beam.
In many machine tools, including lasers used for drilling, cutting or welding, a visible Helium Neon laser beam is used for positioning and alignment of the workpiece by an operator. In addition, many machine tools are equipped with a television camera system to view the machining operation. The present invention utilizes these existing components to provide the "trip" signal input to the positioning system. Thus, the present invention can be installed into an existing machine tool system easily and at a relatively small cost in comparison to a contact probing system.